The present invention relates to a system for the continuous separation of mixtures of complex solutes in aqueous solution by the simultaneous use of annular chromatography and electrophoresis.
The separation of complex aqueous mixtures of solutes is especially difficult to accomplish on a continuous basis. The separation of mixtures of macromolecules such as proteins and synthetic polymers is particularly difficult. In the past, such complex mixtures have been separated, for example, by continuous electrophoresis, which combines effects of fluid flow and electrolyte migration at right angles to an imposed electrical field. See Vermeulen et al, "Design Theory and Separation in Preparative-scale Continuous-flow Annular-bed Electrophoresis," Ind. Eng. Chem. Process Des. Develop. 10(1): 91-101 (1971). According to Vermeulen et al, uniform flow through an electrochromatographic column is achieved by the use of a bed-packing which is comprised of like-sized, spherical particles, that act as an "anticonvectant."
U.S. Pat. No. 3,616,453 discloses a continuous electrophoretic separation device that includes an annular chamber, extending between an outer and an inner cylindrical wall, through which a continuous flow of dilute electrolyte is directed axially. A radial potential gradient is established in the dilute electrolyte, so that components of a complex mixture introduced into the annular chamber migrate radially at differing rates, thereby separating liquid flowing through the chamber into differing radial laminae. At least the outer cylindrical wall is continuously rotated to provide a centrifugal field across the annular chamber which inhibits mixing of these laminae. The inner wall can also be rotated to give an annular separation chamber which is "angular velocity gradient"-stabilized.
U.S. Pat. No. 3,844,926 discloses improved inlet means by which the dilute electrolyte eluant and the mixture to be separated can be introduced into the annular chamber of the above-described separation device. The disclosed improvement does not overcome, however, certain drawbacks to the basic separation device taught by U.S. Pat. No. 3,616,453. First, the disclosed separation system employs a fast-moving rotor to provide the rapid rotation of the cylindrical wall that is necessary to achieve desired fluid dynamic stability in the annular chamber. The requirement for a rapidly moving rotor substantially complicates system design. Second, separation via the disclosed system is essentially one-dimensional, i.e., components of a mixture introduced into the annular chamber can be separated only radially.
Another approach to multicomponent separation on an industrial scale utilizes continuous annular chromatography (CAC). The operation of a continuous, annular chromatograph involves moving an annular bed of sorbent past a stationary feed entry point and stationary effluent recovery ports. As the annulus rotates, material to be separated is introduced, over a short feed-introduction time, followed by a relatively longer period of elution from a series of eluent nozzles. During this operational sequence, the initial entry point completes a revolution. As elution proceeds, the eluted substances progress down the annulus, giving the appearance of helices as the annulus rotates. The more strongly sorbed species exit from the rotating annulus at a greater distance from the feed point, thus providing a continuous "circumferential" separation of species with differing sorption characteristics. See, generally, Scott et al, "Pressurized, Annular Chromatograph for Continuous Separations," J. Chromatogr. 126: 381-400 (1976), the contents of which are hereby incorporated herein by reference. In this fashion, hafnium and zirconium, a system of importance to the nuclear fuel cycle, have been separated. Begovich et al, "Continuous Ion Exchange Separation of Zirconium and Hafnium Using an Annular Chromatograph," Hydrometallurgy 10: 11-20 (1983). Nevertheless, CAC provides, like continuous electrophoresis, only one-dimensional separation capability.